This is a real pain because I had to manually unplug ethernet cables for network testing or to use an alternate network or guarantee physical access to one network segment is cut off.
For some reason this happened after Ikilled dbus because it was confused and blocking packets thinking they were coming from the wrong interface since eth0 and eth1 both had the same subnet and gateway.
I eventually did a "service network-manager restart" but the option was........
It is a permissions issue that is hard to fix.
All but one USB device is greyed out.
I am already a member of "vboxusers"
I have already enabled and disabled USB support for the guest.
I have already reinstalled the latest VBOx guest editions
If running as root it all works fine
The solution is simple but it's a wonder why VBOX doesn't address it directly?
Perhaps newer versions will but you have to add your user to the "vboxusers" group and then login and logout and you'll see the devices you wanted but couldn't access are now available.
The weird thing is that the grayed out issue doesn't happen with all devcies but one notable thing is the Apple iPhone especially in DFU or Recovery Mode which is an big issue for some people.........